U.S. patent number 5,732,375 [Application Number 08/566,029] was granted by the patent office on 1998-03-24 for method of inhibiting or allowing airbag deployment.
This patent grant is currently assigned to Delco Electronics Corp.. Invention is credited to Robert John Cashler.
United States Patent |
5,732,375 |
Cashler |
March 24, 1998 |
**Please see images for:
( Reexamination Certificate ) ** |
Method of inhibiting or allowing airbag deployment
Abstract
An array of pressure sensors on a vehicle passenger seat senses
the presence of an occupant including an infant seat and determines
whether the infant seat faces forward or rearward. A microprocessor
coupled to the sensors determines whether to allow or inhibit
deployment based on the sensor load forces and the pattern of
loading. The pattern can identify an infant seat and pattern and
loading determine its orientation. Local areas are checked to
detect child occupants. Fuzzy logic is used to determine loading
and to recognize patterns.
Inventors: |
Cashler; Robert John (Kokomo,
IN) |
Assignee: |
Delco Electronics Corp.
(Kokomo, IN)
|
Family
ID: |
24261163 |
Appl.
No.: |
08/566,029 |
Filed: |
December 1, 1995 |
Current U.S.
Class: |
701/45; 180/273;
280/735; 701/46 |
Current CPC
Class: |
G06K
9/00362 (20130101); G06K 9/3241 (20130101); B60R
21/01516 (20141001) |
Current International
Class: |
B60R
21/01 (20060101); G06K 9/32 (20060101); G06K
9/00 (20060101); B60R 021/32 (); G06F 017/40 () |
Field of
Search: |
;364/424.055,424.056,424.057,567,568 ;180/271,282,268,273 ;307/15.1
;340/436,438 ;280/735,730.01,730.02 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Research Disclosure--Jan. 1994 #357--"Method for Sensing Occupant
Mass and Position." Disclosed Anonymously..
|
Primary Examiner: Nguyen; Tan Q.
Attorney, Agent or Firm: Navarre; Mark A.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A method of airbag control in a vehicle having an array of force
sensors on the passenger seat coupled to a controller for
determining whether to allow airbag deployment based on sensed
force and force distribution comprising the steps of:
measuring the force detected by each sensor;
calculating the total force of the sensor array;
allowing deployment if the total force is above a total threshold
force;
defining a plurality of seat areas, at least one sensor located in
each seat area;
determining the existence of a local pressure area when the
calculated total force is concentrated in one of said seat
areas;
calculating a local force as the sum of forces sensed by each
sensor located in the seat area in which the total force is
concentrated; and
allowing deployment if the local force is greater than a predefined
seat area threshold force.
2. The method of airbag control as defined in claim 1
including:
determining a pattern of sensor loading;
determining from the pattern of sensor loading whether an infant
seat is on the passenger seat;
then determining from the total force and force distribution
whether the infant seat is facing forward or rearward;
allowing deployment for a forward facing seat; and
inhibiting deployment for a rearward facing seat.
3. The method of airbag control as defined in claim 2 wherein the
step of determining a pattern of sensor loading comprises detecting
which sensors are below a first load threshold and which sensors
are above a second load threshold.
4. The method of airbag control as defined in claim 2 wherein the
step of determining from the pattern of loaded sensors whether an
infant seat is present comprises:
establishing a table of loaded and unloaded sensor patterns which
result from the configuration of the bottom of an infant seat;
and
deciding that an infant seat is present when the pattern of sensor
loading matches one of the table patterns.
5. The method of airbag control as defined in claim 2 wherein the
step of determining whether the infant seat is facing forward or
rearward comprises:
deciding that the seat is facing forward when
1) the total force is greater than a first value, or
2) sensors in the front of the seat are loaded and the total force
is greater than a second value; and
deciding that the seat is facing rearward when both the conditions
1) and 2) are not true.
6. The method of airbag control as defined in claim 1
including:
determining a pattern of sensor loading;
prior to the step of allowing deployment if the total force is
above a total threshold force, determining from the pattern of
sensor loading whether an infant seat is on the seat;
then determining from the total force and force distribution
whether the infant seat is facing forward or rearward;
allowing deployment for a forward facing seat; and
inhibiting deployment for a rearward facing seat.
7. The method of airbag control as defined in claim 1 wherein the
defined seat areas overlap so that some sensors are included in
more than one seat area, the seat areas including a front area, a
rear area, a right area and a left area.
8. The method of airbag control as defined in claim 1 wherein each
of said seat areas includes a secondary group of sensors peculiar
to that seat area and the method includes:
calculating a modified local force for each secondary group located
in a seat area in which the total force is concentrated; and
allowing deployment if the modified local force for exceeds a
threshold for that secondary group.
9. The method of airbag control as defined in claim 8 wherein each
secondary group of sensors comprises a pair and the step of
calculating a modified local force comprises limiting the higher
sensor force to a maximum delta above the lower sensor force and
adding the higher sensor force, as limited, to the lower sensor
force.
10. The method of airbag control as defined in claim 1 including
the steps of:
defining a center seat area including a group of sensors located in
the center of the passenger seat,
calculating a local force for the center seat area as the sum of
the forces sensed by the sensors in the center seat area; and
allowing deployment if the local force for the center seat area is
greater than a predefined center seat area threshold force.
11. A method of airbag control in a vehicle having an array of
force sensors on the passenger seat coupled to a controller for
determining whether to allow airbag deployment based on sensed
force and force distribution comprising the steps of:
measuring the force sensed by each sensor;
calculating the total force of the sensor array;
allowing deployment if the total force is above a total threshold
force;
assigning a load rating to each sensor based on its measured force,
said load ratings being limited to maximum value;
summing the assigned load ratings for all the sensors to derive a
total load rating; and
allowing deployment if the total load rating is above a predefined
total load threshold, whereby deployment is allowed if the sensed
forces are distributed over the passenger seat, even if the total
force is less than the total threshold force.
12. The method of airbag control as defined in claim 11 wherein the
step of assigning a load rating to each sensor comprises:
establishing a base force; and
assigning a load rating according to the measured force minus the
base force.
13. The method of airbag control as defined in claim 11 further
including the steps of:
defining a plurality of seat areas, at least one sensor located in
each seat area;
determining the existence of a local pressure area when the
calculated total force is concentrated in one of said seat
areas;
calculating a local force as the sum of forces sensed by each
sensor located in the seat area in which the total force is
concentrated; and
allowing deployment if the local force is greater than a predefined
seat area threshold force.
14. The method of airbag control as defined in claim 13 further
including the steps of:
determining individual fuzzy values based on the total force, the
local forces for each seat area, and total load rating;
summing said fuzzy values; and
allowing deployment if the summed fuzzy values exceed a
threshold.
15. A method of airbag control as set forth in claim 11, including
the steps of:
determining a fuzzy total force contribution value based on the
calculated total force;
determining a fuzzy total loading contribution value based on the
total load rating; and
summing the fuzzy total force and fuzzy total loading contribution
values, and allowing deployment if the summed contribution values
exceed a predefined fuzzy threshold.
16. The method of airbag control as defined in claim 15 wherein the
steps of determining the fuzzy total force and total loading
contribution values comprises:
setting minimum and maximum thresholds for the total force and
total load rating; and
subtracting the minimum thresholds from the respective total force
and total load rating, and limiting each difference to the
respective maximum threshold; and
determining the fuzzy total and total loading contribution values
based on the respective limited differences.
17. A method of airbag control in a vehicle having an array of
force sensors on the passenger seat coupled to a controller for
determining whether to allow airbag deployment based on sensed
force and force distribution comprising the steps of:
measuring the force sensed by each sensor;
calculating the total force of the sensor array;
allowing deployment if the total force is above a total threshold
force; and
if the total force is not above the total threshold force,
determining a fuzzy total force contribution value based on the
calculated total force;
defining a plurality of seat areas, at least one sensor located in
each seat area, calculating a local force for each seat area as the
sum of forces sensed by each sensor located in that seat area, and
determining a fuzzy local force contribution value based on each of
the calculated local forces; and
summing the fuzzy total force and fuzzy local force contribution
values, and allowing deployment if the summed contribution values
exceed a predefined fuzzy threshold.
18. The method of airbag control as defined in claim 17 wherein the
steps of determining the fuzzy total and local force contribution
values comprises:
setting a minimum and maximum force threshold for each total and
local force; and
subtracting the minimum force thresholds from the respective total
and local forces and limiting each difference to the respective
maximum force threshold; and
determining the fuzzy total and local force contribution values
based on the respective limited differences.
19. The method of airbag control as defined in claim 17 wherein
a pair of sensors are located
in each seat area, and wherein:
the step of calculating the local force for each seat area
comprises the steps of:
limiting the higher force of the respective pair of sensors to a
set amount greater than the lower force of the respective pair of
sensors, and
summing the lower force and the higher force, as limited, to derive
the local force;
and the step of determining a fuzzy local force contribution amount
comprises the steps of:
setting a maximum pair force threshold, and
setting the fuzzy local force contribution amount equal to the
local force limited to the maximum pair force threshold.
Description
FIELD OF THE INVENTION
This invention relates to occupant restraints for vehicles and
particularly to a method using seat sensors to determine seat
occupancy for control of airbag deployment.
BACKGROUND OF THE INVENTION
The expanding use of supplemental inflatable restraints (SIRs) or
airbags for occupant protection in vehicles increasingly involves
equipment for the front outboard passenger seat. The driver side
airbag has been deployed whenever an imminent crash is sensed. The
position and size of the driver is fairly predictable so that such
deployment can advantageously interact with the driver upon a
crash. The passenger seat, however, may be occupied by a large or a
small occupant including a baby in an infant seat. It can not be
assumed that a passenger of any size is at an optimum position
(leaning against or near the seat back). An infant seat is normally
used in a rear facing position for small babies and in a forward
facing position for larger babies and small children. While the
forward facing position approximates the preferred position for
airbag interaction, the rear facing position places the top portion
of the infant seat close to the vehicle dash which houses the
airbag. In the latter event, it is desirable to prevent deployment
of the airbag.
It has been proposed in U.S. Pat. No. 5,474,327 which will issue
Dec. 12, 1995, entitled VEHICLE OCCUPANT RESTRAINT WITH SEAT
PRESSURE SENSOR and assigned to the assignee of this invention, to
incorporate pressure sensors in the passenger seat and monitor the
response of the sensors by a microprocessor to evaluate the weight
distribution and determine the type of occupant and the facing
direction of an infant seat. The sensor arrangement and the
algorithm successfully cover most cases of seat occupancy. It is
desirable, however, to encompass every case of seat occupancy.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to detect a
comprehensive range of vehicle seat occupants including infant
seats for a determination of whether an airbag deployment should be
permitted. Another object in such a system is to determine whether
an infant seat is facing the front or the rear. Another object is
to include sensitivity to the possible seating positions of small
children.
A SIR system, as is well known, has an acceleration sensor to
detect an impending crash, a microprocessor to process the sensor
signal and to decide whether to deploy an airbag, and a deployment
unit fired by the microprocessor. An occupant detection system can
determine if an occupant or infant seat is positioned in a way to
not benefit from deployment, and then signaling the microprocessor
whether to allow or inhibit deploying the airbag.
A dozen sensors, judicially located in the seat, can garner
sufficient pressure and distribution information to allow
determination of the occupant type and infant seat position. This
information, in turn, can be used as desired to inhibit SIR
deployment. The sensors are arranged symmetrically about the seat
centerline and includes a front pair, a right pair, a rear pair, a
left pair and four in the center. Each sensor is a very thin
resistive device, having lower resistance as pressure increases. A
microprocessor is programmed to sample each sensor, determine a
total weight parameter by summing the pressures, and determine the
pattern of pressure distribution by evaluating local groups of
sensors.
Total force is sufficient for proper detection of adults in the
seat, but the pattern recognition provides improved detection of
small children and infant seats. To detect infant seats, all
patterns of sensor loading which correspond to the imprints of
various seats are stored in a table and the detected sensor pattern
is compared to the table entries. Front and rear facing seats are
discriminated on the basis of total force and the loading of
sensors in the front of the seat.
The pattern recognition for detecting children is made possible by
applying fuzzy logic concepts to the pressure readings for each
sensor in the array and assigning a load rating to each sensor.
Pattern recognition is also enhanced by sampling several pairs of
sensors, applying leveling technique to them, and computing a
measure for the area of the seat covered by each pair. For all
measures calculated within the algorithm, a contribution is made to
an overall fuzzy rating which is used to handle marginal cases.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other advantages of the invention will become more
apparent from the following description taken in conjunction with
the accompanying drawings wherein like references refer to like
parts and wherein:
FIG. 1 is a schematic diagram of an SIR system incorporating a seat
occupant detector;
FIG. 2 is a position diagram of seat sensors for the system of FIG.
1, according to the invention;
FIG. 3 is a flow chart representing an overview of an algorithm for
determining deployment permission according to the invention;
FIG. 4 is a flow chart representing a method of computing decision
measures used in the algorithm of FIG. 3;
FIG. 5 is a graphical representation of a function used in fuzzy
logic for total force and load ratings;
FIG. 6 is a graphical representation of a function used in fuzzy
logic for determining load rating;
FIG. 7 is a position diagram of seat sensors illustrating sensor
grouping;
FIG. 8 is a flow chart for deployment decision, according to the
invention; and
FIG. 9 is a flow chart representing the logic for determining the
facing direction of an infant seat as required by the algorithm of
FIG. 8.
DESCRIPTION OF THE INVENTION
Referring to FIG. 1, a SIR system includes a SIR module 13 coupled
to a seat occupant sensing system 14. The SIR module 13 includes an
accelerometer 15 mounted on the vehicle body for sensing an
impending crash, a microprocessor 16 for receiving a signal from
the accelerometer and for deciding whether to deploy an airbag. An
airbag deployment unit 18 is controlled by the microprocessor 16
and fires a pyrotechnic or compressed gas device to inflate an
airbag when a deploy command is received. A fault indicator 20,
also controlled by the microprocessor 16 will show a failure of the
seat occupant sensing system 14.
The seat occupant sensing system 14 comprises a microprocessor 22
having a 5 volt supply and an enabling line 24 periodically
provided with a 5 volt enabling pulse, and a series of voltage
dividers coupled between the enabling line 24 and ground. Each
voltage divider has a fixed resistor 26 in series with a pressure
sensor or variable resistor 28, and the junction point of each
resistor 26 and variable resistor 28 is connected to an A/D port 30
of the microprocessor 22. The microprocessor 22 controls the pulse
on enabling line 24 and reads each sensor 28 voltage during the
pulse period. The microprocessor 22 analyzes the sensor inputs and
issues a decision whether to inhibit airbag deployment and the
decision is coupled to the microprocessor 16 by a line 32. The
microprocessor 22 also monitors its decisions for consistency and
issues a fault signal on line 34 to the microprocessor 16 if faults
continue to occur over a long period.
Each fixed resistor 26 is, for example, 10 kohms and the variable
resistors vary between 10 kohms at high pressure and 100 kohms at
low pressure. Then the voltage applied to the ports 30 will vary
with pressure. Each sensor comprises two polyester sheets each
having a film of resistive ink connected to a conductive electrode,
the two resistive films contacting one another such that the
resistance between electrodes decreases as pressure increases. Such
pressure sensors are available as ALPS pressure sensors from Alps
Electric Co, Ltd, Tokyo, Japan.
The mounting arrangement of sensors 28 on a bottom bucket seat
cushion is shown in FIG. 2. The sensors are numbered 1-12 according
to seat location. A left pair of sensors 1 and 2 are on the left
side of the seat with sensor 2 to the rear and slightly inboard of
sensor 1. Sensors 11 and 12 are the corresponding right pair of
sensors. A front pair of sensors 6 and 7 are at the front of the
seat and a rear pair of sensors 3 and 10 are at the rear. The four
remaining sensors 4, 5, 8 and 9 are the center group of sensors.
Sensors 5 and 8 are astride the seat centerline and are just in
front of sensors 4 and 9. The center group is positioned just to
the rear of the seat middle.
The method of operation is illustrated by a series of flowcharts
wherein the functional description of each block in the chart is
accompanied by a number in angle brackets <nn> which
corresponds to the reference number of the block. The overall
operation is shown in FIG. 3 wherein the sensor values are read by
the microprocessor 22 <36> and the data is adjusted by bias
correction and low pass filtering <38>. One sensor at a time
is turned on, sampled four times and averaged. Then a bias
calibrated for each sensor is subtracted from each sensor reading,
and the data is filtered with a time constant on the order of 1
second. Then all decision measures are computed <40> and
decision algorithms are run <42>. Ultimately a decision is
made to allow or inhibit airbag deployment <44>. Then either
an inhibit light is turned on <46> or an allow light is
turned on <48>.
FIG. 4 shows the algorithm for computing decision measures 40.
Total force is calculated by summing the sensor values and a fuzzy
contribution is calculated for the total force <50>. Each
sensor produces a voltage which is expressed as a digital value in
the range of 0-255. The typical range is on the order of 0-50,
however. An empty seat will have a total force near 0 after the
bias adjustments. A fully loaded seat could go up to about 3000 but
2000 is more likely. For discrimination purposes, the inhibit/allow
threshold is less then 255 and for reporting to the display
software, the value is clipped to 255. The total fuzzy contribution
is determined according to the function shown in FIG. 5. If the
total force is below a minimum or inhibit threshold b, the fuzzy
value is zero; if it is above a maximum or allow threshold, the
fuzzy value is the difference between the inhibit and allow
thresholds; and if it is between the thresholds the fuzzy value is
equal to the force value minus the inhibit threshold. The
thresholds are calibrated for each application; they may be for
example, an inhibit threshold of 32 and an allow threshold of
128.
The next step in FIG. 4 is to determine the load rating of each
sensor <52>. The load rating is a measure of whether the
sensor is detecting some load and is used for pattern recognition
purposes. Low loads present a borderline case which is rated by
fuzzy logic according to a function similar to that of FIG. 5. As
shown in FIG. 6, if a load is below a base value d, which may be
four, the rating is zero and if it is above the base value it is
the difference between the base and the measured load up to a limit
value of, say, four. The total load rating is calculated <54>
by summing the individual sensor ratings and the fuzzy contribution
of the total load rating is again determined as in FIG. 5 where a
total load below a minimum threshold b is zero, a total load above
the minimum is the total load minus the minimum threshold up to a
limit at maximum threshold c. The minimum threshold may be four,
for example, and the maximum threshold may be 24.
Next a check is made for force concentration in a localized area
<56>. Four overlapping localized areas are defined as shown
in FIG. 7. The front four sensors 1, 6, 7 and 12 are in the front
group, the rear eight sensors 2, 3, 4, 5, 8, 9, 10 and 11 are in
the rear group, the left eight sensors 1, 2, 3, 4, 5, 6, 8, and 9
are in the left group, and the eight sensors 4, 5, 7, 8, 9, 10, 11,
and 12 are in the right group. The algorithm determines if the
pressure is all concentrated in one group by summing the load
ratings of the sensors in each group and comparing to the total
load rating. If the rating sum of any group is equal to the total
rating, a flag is set for that group (all right, all front
etc.).
Finally the force and fuzzy contribution is computed for each pair
of sensors and for the center group <58>. The force on each
pair is used to detect occupants such as small children which can
easily sit in one small area of the seat. These measures are
looking for the pressure to be evenly distributed over the two
sensors of the pair. To accomplish this the algorithm looks at each
pair, determines the minimum value of the two sensors, and clip the
higher one to a calibrated "delta" from the lower. If the force is
evenly distributed over the two sensors the values will be about
equal and the sum will be unaffected by clipping. The sum of the
two sensor forces, as adjusted, comprise the force measure of the
pair. The fuzzy contribution of each pair is equal to the force
measure of the pair but limited to a maximum value such as 20 which
is calibrated separately for each pair. The center group measure is
the sum of the sensor forces and the fuzzy contribution is equal to
the sum of the four sensors but limited to a calibrated maximum
value.
______________________________________ SENSOR Pattern 1 2 3 4 5 6 7
8 9 10 11 12 ______________________________________ 1 L L U U L L U
U L L 2 L U U U U L 3 L U U U L U U 4 L L L U L L L 5 L U U U U L 6
U L U U L U U 7 U U L U U L U 8 L U U L L U U L 9 LX L U U L X L 10
L X L U U L X L 11 L L L L 12 L U U L
______________________________________
The measured values, ratings, patterns and flags are used in
deciding whether to allow or inhibit deployment. As shown in FIG.
8, the decision algorithm 42 first decides if rails of an infant
seat are detected <60> and if so whether the seat is facing
forwardly or rearwardly <62>. Deployment is allowed for a
forward facing seat and inhibited for a rear facing seat. This is
determined as shown in FIG. 9 wherein if the total force is greater
than a certain value <64> the seat is forward facing and
deployment is allowed. If not, and the front pair of sensors is
loaded and the total force is greater than another set value
<66>, the seat is forward facing and deployment is allowed.
Otherwise the seat is rear facing and deployment is inhibited. It
should be noted that whenever an inhibit or allow decision is made,
that decision is controlling and all other conditions lower on the
chart are bypassed.
If rails are not detected <60>, the total force is compared
to high and low thresholds <68>. If it is above the high
threshold deployment is allowed and if below the low threshold the
deployment is inhibited. Otherwise, if the localized force for a
sensor group is above a threshold and the flag corresponding to
that group is set <70>, deployment is allowed. If not, the
next step is to compare the total load rating to high and low
thresholds <72>. Deployment is allowed if the rating is above
the high threshold and inhibited if below the low threshold. Each
of the sensor pairs for front, left, right, and rear are compared
to threshold values <74-80>. If any of them are above its
allowed. If not, the center group force is compared to a threshold
<82> to decide upon allowance. Finally, the total fuzzy value
is compared to a threshold <84> to allow deployment if it is
sufficiently high, and if not the deployment is inhibited. The
fuzzy value decision manages a marginal case where several of the
previous measures came close to exceeding their thresholds but
didn't, the fuzzy measure can still allow deployment.
It will thus be seen that airbag deployment can be allowed or
inhibited by a pattern of resistive sensors embedded in a seat
cushion and coupled to a microprocessor to detect the force on each
sensor to determine the loading pattern as well as the force values
from which infant seat presence and orientation are determined as
well as the presence of other occupants.
* * * * *